Dynamic properties of the neuronal cytoskeleton affect many aspects of the nervous system, ranging from generation and maintenance of neuronal morphologies to defining functional domains in a neuron. These require genetic and biochemical adaptations of cytoskeletal elements to specific biological requirements of neurons. Some result from programs initiated during differentiation of neurons and glia, while other represent responses to the local environment and are sensitive to subsequent changes in that environment. A variety of biochemical specializations of the neuronal cytoskeleton have been identified. We have recently demonstrated a novel posttranslation modification of axonal tubulin that may be important in the biogenesis of insoluble tubulin. Experiments in this application seek to characterize insoluble tubulin and to define the physiological roles played by stable axonal microtubule segments in neuronal growth and regeneration. Studies on Trembler and Shiverer mice, two mutant strains with deficient myelination, have begun to characterize the local responses of the axon to different microenvironments. The extent to which the glial environment can alter the organization and dynamics of the underlying axonal cytoskeleton will be examined in demyelinated and myelinated nerves. Interactions between myelinating glia and axons in the CNS and PNS will be characterized to determine the extent to which local modulation of the axonal cytoskeleton by the glial environment sculpts the functional architecture of the axon. Based on our demonstration that demyelination of PNS axons affects the organization and phosphorylation of axonal cytoskeletal proteins. We propose to identify metabolic pathways by which myelination alters cytoskeletal phosphorylation. These experiments will identify mechanisms by which a specific molecular response of the axon to its environment is generated. Our goal is to provide a foundation for understanding neuronal dynamics in development, regeneration, and neuropathology.